From what I can gather the error code relates to a security protocol in Windows 7 that is disabled by default.
Look at the first answer Media Creation Tool - error code 0X80072F8F - 0X20000 - Microsoft Community
and it refers to Update to enable TLS 1.1 and TLS 1.2 as default secure protocols in WinHTTP in Windows - Microsoft Support
It could also be that because Windows 7 is out of support the Media Creation Tool no longer works. Did you try selecting Update now at Download Windows 10 (microsoft.com)
There are other ways of getting an ISO image file, by using TechBench by WZT (v4.1.1) (rg-adguard.net) or using
Rufus Rufus - Create bootable USB drives the easy way
You will need to either create a boot USB for Windows 7 or mount the image file in Windows Explorer, either way you would need to be able to run setup from Windows Explorer.